Frances Melville, who represented a ward in St Andrews for three decades, said she was backing Stephen Gethins to retain his seat in North East Fife.
Gethins held off a Lib Dem challenge by just two votes at the last general election in 2017, and the constituency is the number one Liberal target in December.
Melville, who was elected provost of Fife in 2007 by her fellow councillors, said the SNP candidate deserved to be returned to Westminster.
“I will be voting for Stephen Gethins who, in my opinion, is the best candidate before us,” she told the Courier.
“As an MP for the last four years, Stephen has fought tirelessly for North East Fife and has succeeded in bringing others together across the political divide to oppose Brexit and the damage being done by Boris Johnson’s out of control government.
“At this critical time, we need someone with his experience and approach for the good of everyone here. People need to understand just how important membership of the EU is to North East Fife and Scotland as a whole.”
Mr Gethins said: “I am very grateful to Frances for her support, she is someone who has worked incredibly hard locally and is well respected across the political spectrum.
“Like many who have previously voted Liberal Democrat in this area, Frances has seen how hard SNP MPs at Westminster have worked to be the most effective pro-remain party.”
He claimed that more and more Liberal Democrat voters in the region were voting SNP for the first time.
“North East Fife voted overwhelmingly to stay in the EU and since the result in June 2016, I have worked hard to represent these views and stand up for this area, doing what I can to prevent a disastrous No-Deal Brexit which will be damaging to the whole of the UK,” he said.
“It will impact on local businesses including those involved in our important food and drink industry, as well as our universities, which not only provide vital employment, but are at the forefront of ground-breaking research into diseases like dementia and diabetes.”
A Scottish Liberal Democrat spokesperson said: “Frances Melville has not been politically active for several years. Nevertheless this will be a disappointing intervention to many who worked hard and campaigned on her behalf in the past.
“What North East Fife needs is an MP who will stand up for our place in the EU, not one who will pile chaos on chaos with independence.”